This invention relates to a vehicle periphery visual recognition system for picking up an image in the range in which the visual field of a person in a vehicle is hard to cover.
Further, this invention relates to a camera for picking up images of a plurality of visual fields at the same time and a vehicle periphery monitoring apparatus using the camera.
Still further, this invention relates to a vehicle periphery monitoring system for picking up images of a plurality of different image pickup areas in the periphery of a vehicle and displaying the picked-up images in a cabin.
Hitherto, a visual recognition system has been proposed for picking up an image of a blind spot such as a lower area at the front of a vehicle or a rear area of a vehicle that the visual field of a driver is hard to cover and displaying the image on a display in the vehicle. For example, the Unexamined Japanese Patent Application Publication No. 2000-89301 discloses a visual recognition system that can pick up images of areas in three directions of the lower side at the front of a vehicle and the left and right at the front of the vehicle at the same time. FIG. 6 is a schematic plan view to show the main part of an image pickup unit 100 used with this kind of system. FIG. 7 is a schematic drawing of the image pickup unit 100 shown in FIG. 6 viewed from the right of the image pickup unit 100. FIG. 8 is a side view of a vehicle 101 installing the image pickup unit 100 in a front end part.
As shown in FIG. 6, the image pickup unit 100 comprises a prism 102 shaped roughly like an isosceles triangle in cross section and a retention member 103 for retaining a lens system 105 and an image pickup device 104 of CCD, CMOS, etc. The image pickup unit 100 is disposed with one vertex 102V of the prism 102 directed toward front D1 of the vehicle 101 shown in FIG. 8 and the optical axis (not shown) of the lens system 105 directed toward the front D1. The image pickup unit 100 also comprises a cabinet (not shown for convenience of the description) for accommodating the prism 102 and the retention member 103.
The prism 102 is a columnar body which is shaped roughly like an isosceles triangle in cross section. Light coming from left and right side areas A1 and A2 of the vehicle 101 shown in FIG. 8 is incident on two sides 102L and 102R extending from the vertex 102V. The light incident on the left side 102L from the left side area A2 is refracted in the prism 102, is internally reflected on the right side 102R, is guided into a rear side 102B, and is emitted. On the other hand, the light incident on the right side 102R from the right side area A1 is also refracted, is internally reflected on the left side 102L, is guided into the rear side 102B, and is emitted. Next, the lens system 105 gathers the light emitted from the rear side 102B and forms a light image on the image pickup device 104. The image pickup device 104 executes photoelectric conversion of the light image and outputs an image signal to a controller (not shown) installed in the vehicle through a cable, etc.
FIG. 7 shows the image pickup unit 100 shown in FIG. 6 viewed from the right. As shown in FIG. 7, a bottom 102C of the prism 102 has an inclined end face, and the prism 102 is disposed so as to be upright perpendicularly to a horizontal plane 106 of the vehicle 101. The lens system 105 is disposed with an optical axis 107 thereof directed downward at a predetermined angle with respect to the horizontal plane 106. Accordingly, light coming from a lower area A3 at the front of the vehicle 101 passes through the lower space of the bottom 102C of the prism 102, is formed as an image through the lens system 105, and is received at the image pickup device 104.
The image signals provided by simultaneously picking up the images of the left and right areas A1 and A2 and the lower area A3 at the front of the vehicle 101 are subjected to image processing in the controller (not shown) installed in the vehicle and then are displayed as images on a display (not shown) placed on an instrument panel, etc., in the vehicle 101. FIG. 9 is a schematic drawing to show an example of images 110 displayed on the display. The images in the right area A1, the left side area A2, and the front lower area A3 are displayed in split display areas B1, B2, and B3 of the display. This enables the driver to check the blind spots in the three directions for safety.
However, the described visual recognition system involves a problem of narrow visual field in the vertical direction. This problem will be discussed in detail with reference to FIG. 8. Assume that the image pickup unit 100 shown in FIG. 8 is installed at a position at height L4=0.9 m above ground. 108. In FIG. 8, VV1 denotes a direct vision possible range of the driver in the vehicle 101, HV2 denotes an image pickup possible range of the image pickup unit 100 installed in the front end part of the vehicle 101, and HV3 denotes a required image pickup range required for the image pickup unit 100.
Vertical angle θ1 of the image pickup possible range HV2 is about 19 degrees, vertical angle θ2 of the required image pickup range HV3 is about 54 degrees, and vertical angle θ3 in an invisible range out of the required image pickup range HV3 in the vicinity just below a bumper 101a is about 21 degrees. Front distance L1 from the bumper 101a positioned at the front end of the vehicle 101 to a front end point 109 of the image pickup possible range HV2 is about 3.3 m, front distance L2 in the range of excluding the image pickup possible range HV2 from the required image pickup range HV3 is about 1.0 m, and front distance L3 in the invisible range is about 0.2 m.
Since the image pickup unit 100 in the related art adopts the standard lens system 105 having the viewing angle of horizontal view angle 50 degrees and vertical view angle 38 degrees, the image pickup possible range HV2 is limited and the required image pickup range HV3 is not covered. To adopt a wide-angle lens system to provide viewing angle in the vertical direction, the viewing angle in the horizontal direction is also enlarged and thus the prism 102 shown in FIG. 6 inputs incidence light not totally reflected on the inner face of the side 102L, 102R. Accordingly, the left and right areas A2 and A1 of the vehicle 101 are not displayed at end parts 111R and 111L of the display areas B1 and B2 shown in FIG. 9, and a problem of lowering viewability occurs.
By the way, to internally reflect light on the side of the prism 102, incidence angle φ on the reflection plane needs to satisfy the relation expression of sin φ>1/n, namely, φ>arcsin (1/n) (n: Refractive index of prism 102). For example, if a lens system having horizontal view angle 120 degrees and vertical view angle 90 degrees is adopted and the prism 102 with refractive index n=1.5 is adopted, light incident from the range of horizontal angle 20 degrees on the left and right excluding the image pickup range of horizontal angle 80 degrees at the center is refracted in the prism 102 and is emitted intact to the outside of the prism 102 without being internally reflected on the side 102L, 102R. Therefore, an image of unnecessary light, which is not the image of the left area A2, the right area A1, is displayed in the end area 111L, 111R of the display area B2, B1 shown in FIG. 9. Thus, a problem of becoming very hard to see occurs.
On the other hand, the Japanese Patent No. 3,154,676 discloses a “vehicle-installed camera image combining vision-through apparatus” adopting a very-wide-angle camera having a wide vertical view angle as a related art. The apparatus comprises means for executing vision-through conversion of an image picked up by the very-wide-angle camera in real time, combining a plurality of camera images, and displaying the resultant image on one display. However, the apparatus described in the Japanese Patent No. 3,154,676 requires image memory and complicated circuit configuration for executing vision-through conversion and thus involves a problem of increasing the manufacturing cost.
Further, an apparatus described in the Unexamined Japanese Patent Application Publication No. 2000-89301 is known as a vehicle periphery monitoring apparatus for picking up images of visual fields in three directions at the same time by a single image pickup device.
A camera of the vehicle periphery monitoring apparatus in the related art once internally reflects incidence light from the left and right visual fields in a prism for optical path change and then forms the light as an image on the image pickup device through an image pickup lens and forms incidence light from the front visual field as an image directly on the image pickup device through the image pickup lens without the intervention of the prism, thereby picking up the images of the visual fields in the three directions of the left and right and the front at the same time by the single image pickup device.
However, with the described camera, the incidence light from the left and right visual fields receives the effect of mirror image inversion by one reflection in the prism and is formed as an image on the image pickup device; whereas, the incidence light from the front visual field is not through the prism and thus is formed as an image on the image pickup device without receiving the effect of mirror image inversion. Thus, the images of the left and right visual fields and the front visual field are picked up by the image pickup device with mutually different directions inverted.
Thus, the vehicle periphery monitoring apparatus in the related art needs to comprise processing means for performing partial inversion processing for the image picked up by the image pickup device and needs to apply partial inversion processing to the image portions of the left and right visual fields or the image portion of the front visual field, of the image picked up by the image pickup device for matching the directions of the image portions and eliminating mixing of the normal image and the mirror image for display. Accordingly, the vehicle periphery monitoring apparatus has disadvantage in that the signal processing circuit configuration becomes complicated.
Still further, available as this kind of vehicle periphery monitoring system in a related art is a system for picking up images of image pickup areas in three directions in the periphery of a vehicle and displaying the images of the image pickup areas in the three directions on a single display screen of a display in a cabin. The images of all the image pickup areas in the three directions are always displayed on the display screen of the display during the system operation.
By the way, it may be unnecessary to display the images of all the image pickup areas in the three directions. For example, if the image pickup areas in the three directions contain an image pickup area in the slanting down direction at the rear of the vehicle, the image of the image pickup area needs to be visually recognizable only when the vehicle starts, runs at low speed, etc., and need not be displayed in any other situation.
However, the vehicle periphery monitoring system in the related art always displays the images of all the image pickup areas in the three directions on the display screen of the display and thus the image of an unnecessary image pickup area is displayed depending on the operation state of the vehicle and it becomes hard to visually recognize the necessary images of other image pickup areas as the unnecessary image pickup area image is displayed; this is a problem.